1. Field of Invention
The present invention relates to protective structures for vehicular engine parts, such as for example engine exhaust manifolds that generate substantial heat and vibration during engine operation. More specifically, the invention relates to the fabrication of protective heat shields applied to such engine parts, and particularly for enhancements of insulation layers employed in such shields for reducing transmission of noise and vibration.
2. Description of the Prior Art
The exhaust manifolds of internal combustion engines in today""s modern vehicles can reach under-the-hood temperatures in the neighborhood of 1600 degrees Fahrenheit. Such high temperatures create significant risks of damage to electronic components sharing under-the-hood space with the manifolds. Thus, protection has been provided for such components via use of heat shields designed to at least partially cover up and insulate exhaust manifolds and other heat generating components. In some cases, the shields have been effective to reduce measured temperature levels to within a range of 300 degrees Fahrenheit.
One recurrent shortcoming with respect to current shield designs, however, has been in their inability to reduce or attenuate noise down to satisfactory levels. Generally, the insulation layer is normally the center layer interposed between two metal layers, is relatively thin, and has a relatively high density that is makes it rather stiff. The insulation layer, while often quite adequate to desirably thwart heat transfer at desired values, has been stubbornly insufficient to dampen noise. Unfortunately, the relatively stiff and thin structures for producing heat shields tend to be prone to producing echoes rather than to absorb vibrations and/or noise.
The present invention provides an improved insulated heat shield for a variety of heat generating components, such as engine exhaust manifolds of internal combustion engines, engine mounts, and catalytic converters of exhaust systems. In one described embodiment, a heat shield is formed as a unitary structure adapted for securement via bolted connection to an engine manifold, and includes three layers; an outer metal layer to provide overall structural integrity, a center layer formed of a relatively thick insulation material of relatively low density to isolate heat and to dampen noise, and an inner metal layer adjacent the shielded component for reflecting heat back to the shielded component.
In the described embodiment, the insulated heat shield includes at least one bolt aperture for attachment of the shield to an under-the-hood shielded component, such as an exhaust manifold; the heat shield is attached by bolts to the shielded component. As disclosed, the volume of the insulation layer is expanded by approximately 15 to 20 percent over conventional insulation materials to produce a softer material having lower density but conventional values of mass. The invention provides that desired values of thickness and density of such layers are determined via modal finite element analysis. The relatively thicker insulation layer of the heat shield is more effective to absorb vibration and to attenuate noise. With no increase in mass, the improved insulation layer is generally no more expensive. In the described embodiment, the insulation layer contains cellulose, diatomaceous earth, talc, and fiberglass.